Conventionally, the following technique has been used in various fields, such as clinical examinations, drug discovery research, environmental monitoring, and biochemistry. That is, immobilizing proteins, nucleic acids, sugar chains, cells, etc., to a substrate, and making use thereof to detect, quantify, analyze, etc., a desired substance. This technique is actively studied even today in order to achieve highly accurate and efficient detection, quantification, analysis, and the like.
For example, when proteins, such as enzymes and/or antibodies, are immobilized to a substrate, and the desired substance is detected by using an enzyme reaction or an antigen-antibody reaction with the immobilized proteins, in order to achieve detection with high accuracy and high efficiency, it is important to immobilize the proteins to a substrate while sufficiently maintaining the activity thereof. Aiming to perform such immobilization, a polystyrene affinity peptide that allows the protein to be immobilized to a polystyrene substrate has been reported (Patent Literature 1). It was confirmed that the activity of the proteins, such as enzymes and/or antibodies, was sufficiently maintained even after they had been immobilized to a polystyrene substrate.
Furthermore, as another peptide, an affinity peptide has been reported that can specifically and firmly immobilize a protein to a polycarbonate substrate or a polymethylmethacrylate substrate (Patent Literature 2).
Silicon nitride (Si3N4), which is used as one of such substrates, is also useful as a semiconductor material. Therefore, if a protein can be desirably immobilized to silicon nitride, further development of techniques utilizing a silicon nitride substrate can be expected. However, in examining the interaction between the surface of an inorganic substance and biomolecules, it has been reported that individual amino acids, such as histidine or arginine, adhere to the surface of silicon nitride (Non-patent Literature 1); however, no peptides having an affinity for a silicon nitride substrate have yet been disclosed.